This invention relates to a dual fuel tank system for a vehicle.
Well known are vehicles, particularly working trucks, that are designed with multiple fuel tanks in order to provide an adequate on-board fuel storage capacity. In certain dual fuel tank system applications, such as when a dump truck body or tow truck body is mounted on a vehicle frame, the frame behind the rear wheels must be shortened. This eliminates the ability to use a single rear mounted fuel tank having an adequate capacity. In such situations, a mid-mounted fuel tank in combination with a smaller rear-mounted fuel tank may be used to satisfy the fuel storage capacity demands of the vehicle owner. Therefore, the situation arises where both a single and a dual fuel tank arrangement may be preferable in a given vehicle platform with a single general vehicle frame construction. Additionally, a preference exists to provide the ability to install an auxiliary fuel tank in a vehicle as an option to the purchaser. When dual tanks are used, the tanks are normally provided with individual filler ports or filler pipes. Other designs may incorporate a mechanism for branching multiple filler pipes from one filler port location into each of the fuel tanks. In either case there is generally a fill limiter line associated with each filler pipe involved in fuel fill nozzle shut-offs that requires an additional connection to each fuel tank.
In order to provide an acceptable dual fuel tank arrangement a system must conform to several parameters known generally in the art. Two, that significantly effect the system's physical arrangement, include evaporative emission control requirements placed upon vehicle fuel systems and fuel fill characteristics requirements. In regard to the former, fuel tanks are generally substantially closed to the atmosphere with the exception of a vent that is routed through an evaporative emission control system to collect, store and use evaporated hydrocarbons from the fuel. Therefore, both tanks in a dual system include a provision for connecting to the emission control system. In regard to the latter, the tank system must exhibit acceptable fuel fill characteristics. These include allowing an adequate fill volume rate without excessive spit-back and initiating acceptable fuel fill nozzle shut-off without unacceptable premature shut-offs. These critical considerations must be taken into account when designing a dual fuel tank system.
With a dual fuel tank system, the fuel supply piping may be arranged to alternately draw fuel from one tank or the other. Another method of drawing fuel from multiple tanks is to provide a fuel transfer pump which transfers fuel from the auxiliary fuel tank to the main fuel tank, wherein the fuel system continuously draws from the main fuel tank. The fuel transfer mechanism may be automatic or manually activated.
The fuel supply lines leading from a dual fuel tank arrangement to the vehicle's engine, commonly include a solenoid valve to provide a means of switching to the tank that will be utilized to supply an operating engine's fuel demands. The solenoid valve is generally provided with a remote operating switch accessible from the driver's seat so that the driver may elect to use fuel from either one tank or the other. Previous dual fuel tank applications have generally required the driver of the vehicle to manually switch from the main tank to the auxiliary tank.
Due to the various interfacing requirements, a problem arises when a vehicle is designed to be provided alternatively with either one main fuel tank or a main fuel tank and an auxiliary fuel tank. In a given vehicle platform that is available with a single main fuel tank or dual tanks, the main tank will generally have to be altered to work in conjunction with an auxiliary fuel tank in the dual tank system. A provision must be included to make the required connections to each tank. In addition to the fuel supply lines to the vehicle and the filler pipe there are several connections that are generally made to a fuel tank. In a typical dual tank arrangement, each tank has a fill limiter line connection, an emissions control fuel vapor line connection, a vent line and a fuel return line from the engine.
It is desirable to have the flexibility to design a vehicle with alternative provisions for either a single main fuel tank or a combination main fuel tank with auxiliary fuel tank system. This desire confronts an obstacle when alterations must be made to the main fuel tank to conform it for operation in both types of arrangements. In such situations, the combination of the filler pipe, fill limiter line, emissions control vent line and fuel transfer lines complicate the ability to provide the selective alternative single tank or dual tank arrangement in a single vehicle. The main fuel tank may have to be substantially altered in order to work in conjunction with an auxiliary fuel tank. Therefore, particularly in such a situation, a problem exists.